1. Field of the Invention
The present invention relates to a fluorescent lamp driver circuit, and more particularly to a multi-lamp cold cathode fluorescent lamp (CCFL) driver circuit.
2. Description of Related Art
In a backlight device of a liquid crystal display (LCD), a high-frequency sine wave AC power supply is usually adopted for supplying electric power to drive a cold cathode fluorescent lamp (CCFL) to emit light. Therefore, a DC/AC inverter circuit is demanded for converting energy. The typical CCFL driver circuit usually has a resonance module to convert a DC voltage into an AC voltage for driving the CCFL to emit light. Voltage and current detect circuits are usually used for detecting a driving voltage and a driving current of the CCFL, respectively. A pulse width modulation (PWM) controller receives a voltage detection signal and a current detection signal for stabilizing the illumination of the CCFL and for circuit protection.
Attending with the development of large-scale LCD panels, the number of CCFLs in the backlight device needed to be driven is increased accordingly. The traditional circuit design with single PWM controller and single resonance module to drive single lamp may incur complicated circuits and high costs of such backlight device. To reduce the cost, U.S. Pat. No. 7,291,991 has disclosed a multi-lamp driver circuit to reduce the number of components in the circuit and simplify the circuit design.
With reference to FIG. 1 for a circuit diagram of a multi-lamp driver circuit in accordance with a U.S. patent, the multi-lamp driver circuit includes a PWM controller 10, a resonance module 20, a multi-lamp module including a plurality of lamps L1˜L4, and a switch module 40. The switch module 40 is connected to an input voltage source Vin and is used to control the energy transmitted to the resonance module 20 according to control signals of the PWM controller 10. The resonance module 20 includes two transformers T1, T2 and a plurality of transistor switches. The lamps L1, L2 are connected in series with a secondary side of the transformer T1, and the lamps L3, L4 are connected in series with a secondary side of the transformer T2. Current detectors 32, 34 are serially connected to the lamps L1, L2 and the lamps L3, L4 respectively for detecting a lamp current passing through the lamps L1, L2 and a lamp current passing through the lamps L3, L4 to generate current detection signals IFB1, IFB2. Voltage detectors 36, 38 are connected in parallel with the lamps L1, L2 and the lamps L3, L4 respectively for detecting lamp voltages of the lamps L1, L2 and the lamps L3, L4 to generate voltage detection signals VFB1, VFB2. The PWM controller 10 receives the current detection signals IFB1, IFB2 and the voltage detection signals VFB1, VFB2 for performing feedback control to control the electric power transmitted by the switch module 40 so as to stabilize the light emission of the lamps and to protect the circuit under the abnormal conditions.
In the aforementioned circuit, one resonance module, one current detector, and one voltage detector are used for driving two lamps simultaneously, and one PWM controller is used for controlling the operation of four lamps. Compared with the conventional circuit, the multi-lamp driver circuit has reduced the number of pins of the PWM controller and the number of electronic components, and also simplified the circuit design. However, it is still an important subject for the CCFL driver circuit research to further reduce the number of pins of the PWM controller and the number of electronic components, and to simplify the circuit design.